As the episode begins with Peter's continued disappearance, Walter consoles himself by smoking a strain of marijuana called "Brown Betty."

Most of the episode is then told from his drug-addled perspective, in which Olivia is a 1940s noir detective and Peter is a conman who ran away with Walter's glass heart.

Because Dunham's sister Rachel (Ari Graynor) is unavailable, she brings her niece Ella (Lily Pilblad) to the lab for Walter and Astrid Farnsworth (Jasika Nicole) to look after.

During the investigation, Detective Phillip Broyles (Lance Reddick) leads her to Massive Dynamic, where the CEO Nina Sharp (Blair Brown) informs her that Peter is a conman and industrial spy.

Olivia finds a check signed by Walter Bishop, who in the story, is an inventor that has created "everything that is wonderful in the world" in order to benefit humanity (hugs, rainbows, bubblegum, singing corpses).

Jeff Pinkner stated that the music was not in the original plan for the episode, but was added to fit into Fox's sweeps stunt.

[11] As the episode occurred after the big reveal of Peter's true identity ("The Man from the Other Side"), the writers knew they wanted "Brown Betty" to explore the aftermath from Walter's damaged psyche.

When we realized that the way Walter would deal with such news would be to try to anesthetize himself with copious amounts of marijuana, well, singing and dancing became a natural outcome.

"[15] Music supervisor Charles Scott IV and J.R. Wyman are big Yes fans, and consequently chose the song that appeared in the opening scene.

They debated ways to make it a happier tone, so Wyman added the Observer scene to change the feeling of the episode, and prepare viewers for next week.

[6] As guest actor Leonard Nimoy, who plays William Bell, was unavailable to shoot the brief conversation with Blair Brown's Nina Sharp, the producers knew they wanted to do something a little more creative for the scene.

They talked to cartoonist Frank Miller and hired a special effects school to do all the modeling, which they accomplished based on photos of Nimoy, because the actor could not come in to have his head scanned; he did some voicework however.

"[20] The co-music supervisor, Billy Gottlieb, called the episode a "little mini feature film in the sense that we had a lot of camera performances with the music.

[6] As the original script contained no musical number for Jasika Nicole, she emailed Jeff Pinkner specifically asking him to let her sing, which he then approved.

[22] The producers were initially going to have him sing Django Reinhardt's "Blue Moon", but changed their minds because they thought it would be better to keep the Observer out of the musical aspect of the episode.

[6] On composing the episode's score, Chris Tilton cited Chinatown as a big influence, and commented "the idea was to have this noir feel but still not be totally away from Fringe".

Although initially cringing over the musical premise, Ramsey Isler of IGN called the episode "admittedly fun" because it "gave us an indirect window to view how Walter feels about himself".

[25] In a review of the DVD, another critic from IGN later called it the "worst overall episode" of the season however, asking the question "Musical numbers and Olivia Dunham: who thought this would be a good idea?

"[26] Ken Tucker of Entertainment Weekly was also initially irritated after hearing Fox's musical plans, and consequently gave "Fringe a lot of credit for pulling off this hour so cleverly"[4] Jennifer Walker from TV Fanatic thought the episode was "bizarre" to watch; it "held our interest for the entire 60 minutes, but really failed to introduce any new information about Peter and the unknown man that has crossed into our dimension".

[27] MTV's John Wigler loved the "noir" element, and thought "each and every participating "Fringe" cast member exhibited great musical ability.

She praised the risktaking it took to make the episode "edgy and whimsical, casting aside the concrete conventions of television storytelling...Not only was it entertaining, but it moved the storyline forward on some important emotional fronts, as the characters deal with Peter's disappearance in ways that protect them, but reveal as well".

[22] Andrew Hanson from the Los Angeles Times also was impressed with the cast's singing abilities, and praised the writers' risk-taking: "that just goes to show how well thought out, creative, and just plain fun tonight’s “Fringe” really was.

[32] Tim Grierson of New York Magazine thought the episode turned out to be simply mediocre because "its noir elements weren’t incorporated in a really interesting way, and as for the musical numbers, they tended to be throwaway bits, save for “fictional” Dunham crooning “For Once in My Life” to the seemingly dying “fictional” Peter near the episode’s end".

Grierson continued that "If a show is going to completely throw away its usual rulebook for a fun onetime-only episode, it would be great if the writers could come up with a story as audacious as their premise.

[35] Jeff Jensen of Entertainment Weekly named it the fourth best episode of the series, explaining "The late season lark that officially launched a tradition for similar stunts, the musical film noir homage 'Brown Betty'... was an offbeat gem that expressed all of Fringe's core themes — redemption, connection, rehumanization — and encapsulated the key relationships (the slow-moving Walter-Peter reconciliation; Peter and Olivia's carefully tended soul-deep romance) more poignantly than most on-point episodes of Fringe, and it left fans wanting the show to keep pushing the innovation.

It also gives the audience a refreshing break from some of the high level angst of the end of the season, allowing Peter and Olivia to act out a properly romantic storyline while their characters in the ‘real’ world have been torn apart.